Safety helmets generally reduce effects of impacts to top and/or side of a user's head. Protective headgear often relies upon a hard outer casing with an impact-energy absorbing padding or a strap based suspension placed between the outer casing and the user's head. If a user wearing such hard shell helmet suffers a hard blow to the helmet, the impact of the hard shell meeting a hard surface generates a shockwave and a high impact force, that can be absorbed (to a limited extent) by the inner shock-absorbing material, or the straps in a typical suspension inside the hard casing and in contact with the user's head.
Various mechanisms responsible for brain injuries are understood to include focal type injuries that generally result from a direct impact to the head, sometimes resulting in cranial fracture. Other mechanisms include coup injuries that result from impacts to the same side of the head, whereas, contrecoup injuries result from impacts to an opposite side of the head. At least some injuries result from a displacement, e.g., a linear translation, of the brain within the skull. Still other injuries, including Diffuse Axonal Injuries (DAI), result from a rotational acceleration of the head and/or severe acceleration and/or deceleration that causes traumatic shearing forces, e.g., tissue sliding over tissue. DAI is believed to be one of the most common and devastating types of traumatic brain injury.
Some have disclosed protective helmets including a hard shell and an internal suspensions that include flexible cradle systems. For example, U.S. Pat. No. 2,870,445, to Fisher, discloses protective headgear and lining suspensions that include cradle straps joined together along an upper portion by an adjustment strap offering a flexible internal surface free of rigid projecting blow transmitting elements to cushion a head of a wearer. U.S. Pat. No. 3,054,111, to Hornickel et al., discloses a shock absorbing helmet that includes a head-receiving cradle formed from straps that may cross each other or be joined at their upper ends by a lace that makes the cradle adjustable. U.S. Pat. No. 2,921,318, to Voss et al. discloses a helmet lining that includes several flexible cradle straps extending up into a crown of a protective helmet from circumferentially spaced points around a lower portion. Each strap includes a strip of woven material that necks down as it stretches in reaction to a blow against the helmet. Other web-like support systems that include strips of flexible material that cross each other are disclosed in U.S. Pat. App. Pub. No. 2002/0000004 to Wise et al.
Others have disclosed protective helmets including a hard shell and external features to reduce head injury risk. For example, U.S. Pub. Pat. App. No. 2015/0157080, to Camarillo et al., U.S. Pub. Pat. App. No. 2011/0185481, to Nagely et al., and U.S. Pat. No. 5,581,816, to Davis, disclose wearable devices having force redirecting units connected between an outer surface of a helmet and a shoulder brace for redirecting head impact forces from a wearer's head to another body part. U.S. Pub. Pat. App. No. 2010/0229287, to Mothaffar, discloses an arrangement of straps extending from a helmet to other parts of a body to limit a range of motion of a wearer's head and flexure of their neck.
Still others have disclosed energy absorbing structures for placement along an interior surface of a helmet. For example, U.S. Pat. No. 9,316,282, to Harris, discloses energy absorbing, collapsible disk structures that have collapsible arms around a perimeter of two disks sandwiching that cause an elastic material to stretch, storing kinetic energy from a vertical direction as potential energy in a horizontal direction. U.S. Pat. No. 2,879,513, to Hornickel et al., discloses a crushable block of energy absorbing material disposed in each loop between a lace and an inner end of suspension cradle straps. Energy absorbed in crushing the blocks reduces the shock of an impact against a wearer's head. U.S. Pat. App. Pub. No. 2009/0260133, to Del Rosario, discloses an impact absorbing frame and multi-layered structure that includes inner opposite-facing inner panels that undergo elastic deformation and compress and expand to dissipate impact energy. U.S. Pat. No. 9,314,063, to Bologna et al., discloses a protective football helmet having a one-piece molded shell with an impact attenuation member formed by removing material from a front portion of the shell to form a cantilevered segment.
Although these and other conventional helmet liners have worked well, they have failed to provide protection against both high and low degrees of impact imparted on a helmet over the extended life of the helmet. The impact force is often so great that the user's helmet may even initially bounce back upon impact, thrusting the user's head away from the blow, subjecting the head and neck regions to additional injury causing forces. If the impact is severe enough, it may lead to a concussion (striking of the brain matter to the skull with moderate force) or worse. In some instances, a user can experience a, so called, focal type of injury, e.g., resulting from a lateral movement of head when shell impacted, alone or in combination with a rotation of the head, in which the head experiences a rapid acceleration and/or deceleration.